Security enclosure manufacture

ABSTRACT

A security enclosure (20) includes an inner enclosure defined by a first electrically insulating sheet (60) carrying a layer (56) of electrically responsive material on an outer side, the sheet (60) being folded and having edges (100) in overlapping relation and adhered to one another to define the inner enclosure. A detector (80) is provided for detecting separation of the electrically responsive material (56) from the sheet (60) and is located inside the inner enclosure. An outer enclosure is defined by a second electrically insulating sheet (44) wrapped about and adhered to the inner enclosure and also having edges in overlapping relation.

FIELD OF THE INVENTION

This invention relates to the manufacture of security enclosures, andmore particularly, but not exclusively, to the manufacture of securityenclosures for giving warning, or destroying or erasing information, ifinterference is made with the enclosure with the aim of gaining accessto an object within the enclosure. The invention has particularapplication to security enclosures having walls formed of flexiblelaminates which have been folded to form the enclosures.

BACKGROUND OF THE INVENTION

It is known to provide security enclosures with walls or sheetsincorporating coils, meshes or grids of electrically responsive materialand to monitor certain electrical characteristics of the material toprovide an indication when the sheet containing the material has beenpierced or an attempt has been made to open the enclosure through othermeans. Detection of such an attempt may activate an alarm, destroy thematerial or object within the enclosure, or erase information if theobject within the enclosure, for example, contains sensitivemagnetically recorded information. Examples of such enclosures aredisclosed in PCT International Application Publication No. WO87/06749 toWolf, U.K. Patent No. 1,375,926 to GAO Gesellschaft Fur Automation undOrganisation mbH, U.S. Pat. No. 4,785,743 to Dalphin and European PatentPublication No. 277,679 to Seculock BV. However, the present inventionis more closely related to security enclosures of the form disclosed inU.K. Patent Application No. GB 2220513A, to W. L. Gore and Associates,Inc. The disclosed security enclosures are formed from layers offlexible material including a matrix of diagonally extendingsemi-conductive lines printed onto a rectangular thin insulating film.The matrix of lines forms a continuous conductor which is broken ifattempts are made to penetrate the film. The circuit is monitored byopening the conductor at one point and measuring the change ofresistance between the two ends of the circuit.

The Gore security enclosure also includes a further protective laminatecomprising two flexible layers of semi-conductive fibrous materialseparated by a layer of insulating material. The lengths of the fibresof the fibrous material are greater than the thickness of the layer ofinsulating material so that piercing the enclosure forces fibres fromone fibrous layer to penetrate the insulating layer and contact theother fibrous layer to produce a detectable change in an electricalcharacteristic of the layers.

Further, the Gore application discloses enclosures in the form ofshallow, rectangular envelopes formed simply by folding the rectangularlaminate about a single axis and then securing the edges of the laminateto one another to form the envelope.

Security enclosures in the form of wedge-shaped, cuboid and cube formare disclosed in U.K. Patent Application GB 2258075A (W. L. Gore &Associates (UK) Ltd). in which a laminate is folded about a plurality offold lines to form the enclosures. This facilitates formation ofenclosures for containing objects that are other than thin and flat.

Further improved security enclosures are also described in the W. L.Gore & Associates (UK) Ltd. U.K. Patent Applications GB 2256956A, GB2256957A and GB 2256958A, each of which describes features forincreasing the difficulty of gaining unauthorised access to theenclosure. In GB 2256956A two layers of semi-conductive fibrous materialare separated by a layer of auto-pyrotechnic insulating material. Inaddition to detecting physical penetration, as discussed above withreference to GB 2220513A, if a laser or other elevated temperaturecutting means penetrates the layers the laser ignites theauto-pyrotechnic material and the subsequent decomposition of the layerwill result in the fibrous layers coming into contact with one another.

In GB 2256957A, a matrix of semi-conductive lines is printed on a thininsulating film, the matrix of lines forming a plurality of conductorswhich are individually monitored. The lines extend over both sides ofthe insulating film and are joined at the edges of the film to definethe conductors, each of which comprises a large number of line segments.The configuration of the connections between the lines may be variedsuch that the conductors may be formed of different configurations oflines. Thus, it would be difficult for an intruder to predict thecombination of line segments which defined a particular conductor. Inthe preferred embodiment each conductor is of the same electrical lengthsuch that the configuration of the connections between the conductorsand a monitoring circuit may also be varied, further increasing thedifficulty of gaining access to the enclosure by isolating individualconductors from the monitoring circuit.

In GB 2256958A a low tensile strength layer is provided between amonitored conductor and a first insulating film, and a second insulatingfilm is adhered over the conductor. An attempt to remove the secondinsulating film to gain access to the conductor results in break-up ofthe low tensile strength layer and detectable damage of the conductor.

The preferred embodiment described in GB 2256958A also includessemi-conductive fibrous layers separated by an insulating layer asdescribed in GB 2220513A. However, in addition, two layers ofsemi-conductive low melt material are provided, one on each side of theinsulating layer. If an attempt is made to penetrate the laminate usinga laser the low melt material will melt and flow through any breaks inthe insulating layer to form a detectable electrical connection betweenthe semi-conductive fibrous layers. A similar arrangement is alsodescribed in European Patent Application No. 0459838.

When forming an enclosure from such laminates it is of course necessaryto overlap edges of the laminates to define the enclosure. To ensure thesecurity of the enclosure the overlapping edges must be carefully formedsuch that separation of the edges, held together by an adhesive, doesnot permit unauthorised entry to the enclosure. An example of anoverlapping edge configuration is disclosed in GB 2256958A (FIG. 3) inwhich the layers of the laminate are feathered and an additional layerof low tensile strength material is provided below conductive linesprovided at one of the edges. While providing a secure join, thenecessity to feather the edges of the various layers of the laminate andprovide additional layers of material at the edges of the laminate addsto the complexity and expense of forming the enclosure.

Further, when forming box-like security enclosures, such as described inGB 2258075A, it is desirable to fold the laminate on itself to allow thecreation of corners between walls of the enclosure. It would of coursebe possible to form the laminates such that such folding was notrequired, for example by utilising a cruciform-shaped laminate to form acuboid enclosure, though this would increase the difficulty of formingthe layers on the laminate, particularly the lines which form theconductors, due to the more complex shapes which would be required, andwould produce less secure areas in the enclosure between the edges ofthe laminate which would be brought together to define the corners ofthe enclosure. Thus, folding the laminate on itself is considered adesirable step, though there are still potential weak spots at suchfolds, for example where electrically insulating layers are broughttogether, as the layers could possibly be separated without damaging thedetecting layers which lie below the insulation. Where two electricallyresponsive layers of lines would otherwise be brought together byfolding, one half of each portion may be provided without such lines asproposed in GB 2258075A, though this increases the difficulty of formingconductors formed of such lines due to the more complex shapes which arerequired.

It is among the objects of the present invention to provide a method offorming a security enclosure defined by a laminate with overlappingedges in which such edges are secure and may be formed relativelyeasily.

SUMMARY OF THE INVENTION

According to the present invention there is provided a method of forminga security enclosure comprising the steps:

providing a first electrically insulating sheet carrying a layer ofelectrically responsive material on one side;

providing detection means for detecting separation of the electricallyresponsive material from the sheet;

connecting said detection means to the layer;

folding said first electrically insulating sheet to define an innerenclosure with said electrically responsive layer extending over anexternal surface thereof and said detection means located therewithin;

providing a second electrically insulating sheet;

providing adhesive on at least one of said external surface of the innerenclosure and said second electrically insulating sheet; and

wrapping said second electrically insulating sheet about said innerenclosure to encapsulate said inner enclosure.

To gain entry to a security enclosure formed by this method, other thanby cutting through the sheets and the electrically responsive layer, itwould be necessary to separate the second electrically insulating sheetfrom the first electrically insulating sheet. If an attempt was made topeel back the second sheet separation would result in break up of theelectrically responsive layer as the sheets were pulled apart. Suchdamage would be detected by the detection means.

Preferably, a low tensile strength material having lower cohesion thanadhesion is located between the first electrically insulating sheet andthe electrically responsive material.

The layer of electrically responsive material may be continuous ordiscontinuous. Preferably, the electrically responsive material isprovided in the form of one or more lines.

Preferably also, adhesive material is provided at selected edge portionsof said first electrically insulating sheet and on folding said sheet todefine the inner enclosure said selected edge portions are placed inoverlapping relation.

Preferably also, said second electrically insulating sheet is wrappedabout said inner enclosure with edge portions of said secondelectrically insulating sheet in overlapping relation.

For use in forming a box-like enclosure, the method of the presentinvention preferably comprises the further steps of:

providing the first electrically insulating sheet with electricallyresponsive line carrying major wall forming portions and intermediatewall forming portions located between the major wall forming portions;

folding said intermediate wall forming portions to permit said majorwall forming portions to define corners of a box-like enclosureincluding folding of selected intermediate wall forming portions toproduce electrically responsive line to electrically responsive lineinterfaces;

providing first wings of electrically insulating sheet extending beyondan area of said first electrically insulating sheet carrying saidelectrically responsive line; and

locating said first wings between said folded selected intermediate wallforming portions to provide electrically responsive line to electricallyinsulating material interfaces therebetween.

The provision of the first wings prevents electrical contact between theelectrically responsive line carrying intermediate wall formingportions. It would be possible to produce a somewhat similar effect byproviding areas of the intermediate wall forming portions without theelectrically responsive line though this would greatly increase thecomplexity and difficulty in forming such a line, and which difficultywould be greatly increased where it was desired to provide a pluralityof lines to form a plurality of monitored conductors and it was desiredthat the conductors of would have the same electrical characteristics orlength.

It is also preferred that the method includes the further steps: offolding further selected intermediate wall portions to produceelectrically insulating material to insulating material interfaces;providing second wings of electrically insulating sheet carryingportions of said electrically responsive line; and locating said secondwings between said folded further selected intermediate wall portions toprovide electrically responsive line to electrically insulating materialinterfaces therebetween.

This arrangement allows the enclosure to be formed without theoccurrence of insulating material to insulating material interfaces atsensitive areas of the enclosure. Such interfaces could facilitateunauthorised entry to the enclosure as the layers of insulating materialcould be separated without causing damage to the electrically responsiveline carried on the other sides of the sheet. In practice, it isdesirable to minimise the number of such second wings as their presenceincreases the complexity of formation of the electrically responsiveline on the insulating sheet.

Preferably also, the method includes the further steps of:

providing said first electrically insulating sheet with lines ofelectrically responsive material on each side, the lines on one sideextending obliquely relative to the lines on the other side and thelines being interconnected at edge portions of the sheet to form aplurality of conductors so dividing the sheet into a number ofrelatively small areas that attempted penetration of the sheet damagesone or more lines, one edge portion of the sheet including a pluralityof line switch means;

selectively configuring the switch means to connect each one of thelines on one side of the sheet with a selected one of a plurality oflines on the other side of the sheet; and

connecting ends of the conductors to the detecting means for detectingdamage to the lines.

The provision of the line switch means permits the configuration of theconductors to be varied such that a detailed examination of one securityenclosure would not enable a potential intruder to predict the paths ofthe conductors of another, similar, security enclosure.

Preferably also, the overlapping edge portions of the secondelectrically insulating sheet are formed on the inner enclosure spacedfrom the overlapping edge portions of the first electrically insulatingsheet. This arrangement increases the difficulty of gaining unauthorisedentry to the enclosure by separation of the sheets. With thisarrangement it would be necessary to first separate the overlappingedges of the second sheet, then separate the second sheet from the firstsheet until the overlapping edges of the first sheet were exposed, andthen separate the overlapping edges of the first sheet before entry tothe enclosure was possible. The areas of separation required to achievethis would be relatively large thus increasing the likelihood ofdetection of the attempt to gain entry by the separation detectionmeans.

Preferably also, the overlapping edge portions of the first electricallyinsulating sheet and the overlapping edge portions of the secondelectrically insulating sheet are formed of opposite hand. With thisarrangement, the second sheet must be separated from the first sheet tothe most distant edge of the inner overlap before an attempt is made toseparate the overlapping edges of the first sheet, thus increasing thedegree of the separation of the layers required to gain access to theinner overlap.

In accordance with a further aspect of the present invention there isprovided a security enclosure comprising:

an inner enclosure defined by a first electrically insulating sheetcarrying a layer of electrically responsive material on an outer sidethereof, the sheet being folded and having edges in overlapping relationand adhered to one another to define the inner enclosure;

detecting means for detecting separation of the electrically responsivematerial from the sheet and said means being located inside said innerenclosure; and

an outer enclosure defined by a second electrically insulating sheetwrapped about and adhered to said inner enclosure and having edges inoverlapping relation.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the present invention will now be described,by way of example, with reference to the accompanying drawings, inwhich:

FIG. 1 is a perspective view of a security enclosure in accordance witha preferred embodiment of the present invention.

FIG. 2 is a plan view of an outer protection layer of the enclosure ofFIG. 1.

FIG. 3 is a plan view of an inner protection layer of the enclosure ofFIG. 1.

FIG. 4 is a sectional view of a portion of the enclosure of FIG. 1.

FIG. 5 is an enlarged sectional view of a wall of the enclosure of FIG.1, showing various layers of the enclosure separated.

FIG. 6 is a plan view of an edge portion of one of the layers of theenclosure wall.

FIG. 7 is a sectional view on line 7--7 of FIG. 6.

FIG. 8 is an enlarged plan view of an edge portion of the layer of FIG.3.

FIG. 9 is a schematic representation of a detection circuit of theenclosure of FIG. 1.

FIG. 10 is a sectional view of a wall of a security enclosure inaccordance with another embodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Reference is first made to FIGS. 1 and 2 of the drawings which shows asecurity enclosure 20 in the form of a cuboid-shaped box having upperand lower walls 22, 24, side walls 26, 28 and end walls 30, 32. Theenclosure 20 comprises two flexible sheets or laminates which are formedas planar sheets and then folded to the desired form. FIG. 2 of thedrawings shows the sheet which forms an outer wrapping for the enclosure20, while FIG. 3 of the drawings illustrates the laminate 36 over whichthe sheet 34 is wrapped. The parts of the sheet and laminate 34, 36which form the walls of the enclosure 22, 24, 26, 28, 30, 32 areidentified by the reference numeral of the particular wall shown inparenthesis. The laminate 36 comprises various layers which areconstructed to detect an attempt to penetrate the enclosure 20. Variouselectrical characteristics of the laminate 36 are monitored by means ofa suitable electrical circuit, as will be described, and any attempt topenetrate the laminate or separate the sheet 34 from the laminate 36results in a change in an electrical characteristic which is detectedand used to activate an alarm, or destroy or erase information from theobject contained within the enclosure 20.

In this particular example the object within the enclosure 20 is akeypad and the sheet 34 is marked with numerals and signs correspondingto the keypad configuration.

The enclosure 20 is formed by first folding the laminate 36 alongvarious fold lines 38 to define a box-shaped inner enclosure. Adhesiveis provided at the overlapping edges of the laminate to form secureoverlaps 40, one of which is illustrated in FIG. 4 of the drawings. Theadhesive coated sheet 34 is then wrapped over the adhesive coated innerenclosure formed by the laminate 36 and similarly arranged with edges inoverlapping relation to encapsulate the inner enclosure. An overlap 42formed at edges of the sheet 34 is also illustrated in FIG. 4.

FIG. 5 of the drawings is an enlarged and somewhat schematiccross-sectional view of the sheet 34 and laminate 36 and illustrates thevarious layers which make up the sheet and laminate. The sheet 34comprises an insulating sheet, in this example a polyester film 44,having a film of adhesive 46 on the inside face. The adhesive 46 is ofpressure sensitive, heat reflowable adhesive, preferably a high vinylacetate VA content ethylenevinyl acetate EVA, for example 70% of VA andalso pigmented black.

The laminate 36 is considerably more complex and is shown separated intothree layers which, for ease of reference, will be referred to as thetamper detect layer 48, the laser detect layer 50 and the pierce detectlayer 52. It should be noted that, with regard to the present invention,it is the tamper detect layer 48 of the laminate 36 which is of primaryimportance. An enclosure within the scope of the invention may be formedwithout the laser detect layer 50 or the pierce detect layer 52, or withthese layers 50, 52 replaced with layers of different configurations asdescribed in the aforementioned patent applications.

The tamper detect layer 48 comprises an adhesive layer 54, lines ortracks of conductive material 56, a low tensile strength material 58having lower cohesion than adhesion, an electrically insulatingpolyester film 60, further conductive tracks 62 and then a furtherinsulating polyester film 66 sandwiched between two adhesive layers 64,68 which serve to secure the tamper detect layer 48 to the laser detectlayer 50.

The adhesive layers 54, 64, 68 are preferably of similar adhesive to theadhesive 46. The tracks 56, 62 are formed of semi-conductive ink, mostpreferably comprising a matrix of low molecular weight polyester resinfilled with carbon and graphite. Typically each track 56, 62 may beformed with a resistivity of 6 ohms/cm for 25% carbon loading inpolyester and is applied by screen printing to a dry thickness ofapproximately 10 microns.

The low tensile strength material 58 is somewhat similar to the adhesiveused to form the layers 46, 54, 64, 68 and as such may comprise anethylvinyl acetate (EVA) having a high vinyl acetate (VA) content, forexample 70% VA, also filled to 45-60% (by weight EVA) with fumed silica(typically having particle size of 12 nm and 20 m² /g surface area).Like the adhesive layers, the material 50 preferably contains a blackpigment such that the carbon-loaded tracks 56 are not easily visible onthe material 58.

When the sheet 34 and laminate 36 are laminated together, preferably ata temperature within the range 60° to 80° C., the two layers of adhesive46 and 54 become homogeneous after a time, typically one or two days.

The materials which form the adhesive layers and the low tensilestrength material are selected to be chemically different from theconductive tracks such that only moderate carbon migration takes placefrom the tracks to the adjacent layers.

The tracks 56, 62 extend diagonally across the film 60 and the tracks onone side extend obliquely relative to the tracks on the other side todivide the film into a matrix 65 (FIG. 8) of diamond shaped areas. Eachtrack 56, 62 terminates at an edge portion of the film 60, in a point orpad 70 (FIG. 6), the pad on each side being in register with a pad onthe other side of the film. Two pairs of registering pads 70a, 70b maybe seen in FIGS. 6 and 7 of the drawings. A connection between thetracks is provided at the pads 70a by forming a hole 72 through thelayer 58 and film 60 such that when the tracks 56, 62 are formed,preferably by printing, the semi-conductive ink used to form the trackson one side extends through the hole 72 into contact with the tracks onthe other side. In practice, the tracks are printed on one side of thefilm before the holes are formed. The holes are then punched in the filmand the connecting hole lining 74 is formed when the second set oftracks are printed on the other side of the film. The matrix of tracks56, 62 are so connected to form a number of loops or conductors, whichwill be broken if an attempt is made to penetrate the film. It will beseen that the pads 70b are devoid of a through hole such that there isno interconnection between lines at the pad 70b.

In this particular embodiment of the present invention the tracks 56, 62are configured to define four conductors or loops. As will be described,the configuration of tracks which form the conducting loops may bevaried such that examination of one security enclosure would not revealthe loop configuration of another similar security enclosure. Also, theconnections between the loops and the detection circuit may be variedfor different enclosures thus increasing the difficulty in gainingunauthorised entry to the enclosure. FIG. 8 of the drawings illustratesone end of the laminate 36 where the end of each track 56, 62 isprovided with five pads. Further, the connection between the tracks andthe detection circuit (FIG. 9) is through connecting means in the formof a matrix of conducting paths 76 which are connected to connectors 78for linking with the detection circuit.

FIG. 9 of the drawings illustrates the circuit 80 which detects changesin the electrical characteristics of the laminate 36. The blocks LA, LB,LC, LD represent the four loops formed by the tracks 56, 62 printed onthe film 60. In this particular example the loops are connected inseries between reference potentials Vo, Vs and V+. Connections are madebetween each loop and a comparator circuit 88 which is set to detect anychange in the monitored potentials Vs-, Vs+, in this particular example,the end of the first loop LA and the beginning of the second loop LB andat the end of the third loops LC and the beginning of the fourth loopLD. Any damage to the loops LA, LB, LC, LD will result in a change inthe monitored potentials Vs-, Vs+, creating an output from thecomparator circuit 88 which may be passed to a suitable amplifier, toactivate an alarm or some other appropriate action.

Referring once more to FIG. 8, the conducting paths 76 comprise, withreference to this particular illustration, a series of longitudinalpaths 94 on the upper surface of the film 60 and a series of lateralpaths 96 on the underside of the film. The lateral paths 96 pass beneaththe connectors 78 and electrical connection between selected ones of theconnectors 78 and the lateral conducting paths 96 are made in the samemanner as the connections at the pads, that is by forming a hole throughthe film at the intersection of the paths 96 and connectors 78 andprinting one of the tracks such that the conducting ink extends throughthe hole to form a connection between the tracks. Connections betweenthe lateral paths 96 and the longitudinal paths 94 are achieved by thesame means.

The longitudinal conductive paths 94 alternate between longer paths 94awhich extend to contact the pads 98a at the extreme edge of the matrix65 formed by the tracks 56 and shorter paths 94b which terminate at endpads 98b directly above pads provided at the ends of alternativeconductive tracks 62 on the underside of the film 60.

It will be noted that there are a great number of possible connectionswhich may be made between the paths 94, 96 and the matrix 65. Thisfacility allows the manufacturer to vary the connections between thematrix 65 and the paths 94, 96 and thus the connections between thematrix 65 and the connectors 78. Thus, if reference is also made to FIG.9, each of the loops LA, LB, LC, LD could be represented by any one ofmany configurations of tracks 56, 62 on the sheet and thus it would beextremely difficult for an intruder to predict the path of a particularloop, and its particular reference potentials, from an examination ofeven a large number of enclosures provided with similar laminates.

To allow use of a similar comparator circuit 88 for each sheet producedit is necessary that the total length of each loop, however formed onthe film 60, be of similar length such that the resistance or change inpotential across each loop is the same and the loops may therefore be"located" in any desired position relative to the comparator circuit 88.

The configuration of the laminate as illustrated in FIG. 8 furtherprovides for the configuration of loops to be varied as each track 56 onone side of the film 60 may be connected to one of five tracks 62 on theother side of the film 60 by providing line switch means in the form ofa line connection through the film 60 between the line 56, 62 by any oneof five pads provided at the edge of the matrix 65. When combined withthe matrix of connecting paths this feature allows many permutations ofloops to be provided, each loop being at one of four different referencepotentials.

Reference is once more made to FIG. 5 and particular reference is madeto the low tensile strength layer over which the conductive tracks 56are printed. An attempt to remove the sheet 34 from the inner enclosureby peeling back the sheet 34 would thus result in breakup of the lowtensile strength layer 58 and damage to the tracks which damage would bedetected by the detection circuit. The laminate 36 is arranged such thatthe tracks 56 and low tensile strength layer 58 extend over the wholesurface of the inner enclosure and an attempt to separate the sheet 34at the laminate 36 at any location on the enclosure is likely to damagethe tracks 56. While this arrangement is straightforward to create atthe majority of overlapping edge portions, such as the overlap 40illustrated in FIG. 4, the formation of the corners betweenperpendicular wall portions of the laminate 36 is not sostraightforward, as will be described.

If reference is made to FIG. 3 of the drawings, nine major wall carryingportions 100 are provided and defined by the fold lines 38. These wallforming portions 100 carry the conductive tracks 56, 62 and in theenclosure 20 will form parts of the enclosure walls. Between the majorwall forming portions 100, and also carrying the conductive tracks 56,62, are a number of intermediate wall forming portions 102 which arefolded in on themselves to permit the adjacent major wall formingportions 100 to be folded into positions where the portions 100 lieperpendicular to one another. To ensure that no shorting occurs betweenthe tracks 56 on parts of each intermediate wall forming portion 102, awing 104 of insulating film is provided adjacent each portion 102 whichmay be folded and located between the parts of the portion 102 toprovide a conductive track to insulating material interface. In thisexample the wings 104 are either triangular or chevron-shaped.Similarly, at two locations the flaps formed by folding the intermediatewall forming portions 102 will be folded and adhered to an adjacentportion of the inner enclosure. This would normally result in aninsulating material to insulating material interface and to avoid thissecond triangular wings 106, which carry conductive tracks 56, areprovided to allow the formation of conductive track to insulatingmaterial interfaces. With the particular laminate configuration asillustrated in FIG. 3 only two secondary wings 106 are necessary, theremainder of the area which carries conductive tracks 56, 62 beingrectangular. This considerably simplifies the manufacture of thelaminate.

The first wings 104 are simply extensions of the film 60 while thesecond wings 106 may consist of extensions of the film 60 and tracks 56or may include the complete three layers 48, 50, 52.

Reference is now made once more to FIG. 5 of the drawings to describethe laser detect and pierce detect layers 50, 52. The laser detect layer50 is formed of two similar parts 108, 110 and the inner part 110 willbe described as exemplary of both. The part 110 includes a plurality ofconductive tracks 122, 126 printed on either side of an insulating film124. The film 124 is mounted on a further insulating film 130 andsecured thereto by an adhesive layer 128. A further adhesive layer 132is provided for securing the layer 50 to the layer 52. The tracks 122,126 on each side of the film 124 extend in parallel and are of a widthand pitch, for example 250 microns wide with a pitch of 500 microns suchthat piercing of the part 110 at any point would result in damage to atleast one of the sets of tracks 122, 126. The tracks 122, 126 eachdefine conductors and are connected to the detection circuit 80. Theupper part 108 is essentially identical to the inner part 110 though isarranged such that the tracks 123, 127 extend perpendicular to thetracks 122, 126 (although not being shown in this manner in FIG. 5) toensure complete coverage by one or more of the tracks 122, 126, 123,127.

The pierce detect layer 52 is as described in GB 2256958A in that itcomprises two layers of fibrous semi-conductive material 136, 148adhered by adhesive 138, 146 to an insulating film 142. In addition,layers of semi-conductive low melt material 140, 144 are providedbetween the fibrous layers 136, 148 and the insulating film 142. Thelengths of the fibres of the fibrous material are greater than thethickness of the layer of insulating film 142 so that piercing theenclosure forces fibres from one fibrous layer 136 to penetrate theinsulating film 142 and contact the other fibrous layer 148 to produce adetectable change in an electrical characteristic of the layers 136,148, which are connected to the detection circuit 80.

Further, if a laser or other elevated temperature cutting meanspenetrates the layers the low melt material 140, 144 will melt and flowthrough any breaks in the insulating film 142 to form a detectableelectrical connection between the semi-conductive fibrous layers 136,148.

A further layer of insulating film 152 is fixed to the inner fibrouslayer 148 using adhesive 150.

In practice, the layers 48, 50, 52 will be manufactured individually andthen bonded together to produce the laminate 36. The laminate is thenfolded about the fold lines 38 to create the inner enclosure. The sheet34 is then wrapped over the inner enclosure. If reference is made inparticular to FIG. 4 of the drawings, it will be noted that the overlaps40, 42 of the edges of the laminate and sheet 36, 34 are at spacedlocations on the enclosure walls. With this arrangement an intruderwishing to gain access to the laminate overlap 40 must first peel backthe sheet 34 over a considerable area of the laminate before reachingthe edge of the overlap 40. Further, it will be noted that the overlaps40, 42 are of different hand which further increases the degree ofseparation necessary to reach the edge of the inner overlap 40.

It will also be noted that separation of the edges of the laminate 36 atthe overlap 40 requires the insulating film 152 to be separated from theouter surface of the tamper detect layer 48 which carries the conductivetracks 56, such that in the attempt of separation would result in damageto the tracks 56.

Reference is now made to FIG. 10 of the drawings which illustrates afurther embodiment of the present invention in which the overlap 240 ofa laminate 236, similar to the laminate 36 described above, has beenrendered more secure by extending the tamper detect layer 248 to form anoverlap portion 241 and to provide an additional protective layer tofurther protect the exposed edge of the laminate 236, which an intrudermight otherwise be able to gain access to by cutting through the sheet234 at the point marked C.

From the above description it will be clear to those of skill in the artthat the method of producing a security enclosure described above, andthe security enclosure which is produced by the method, offer improvedprotection against unauthorised entry to the enclosure. It will also beclear to those of skill in the art that various modifications andimprovements may be made to the described embodiments without departingfrom the scope of the invention.

I claim:
 1. A method of forming a security enclosure (20) comprising thesteps:providing a first electrically insulating sheet (60) carrying alayer (56) of electrically responsive material on one side; providingdetection means (80) for detecting separation of the electricallyresponsive material from the sheet (60); connecting said detection means(80) to the layer (56); folding said first electrically insulating sheet(60) to define an inner enclosure with said electrically responsivelayer (56) extending over an external surface thereof and said detectionmeans (80) located therewithin; providing a second electricallyinsulating sheet (44); providing adhesive material (46, 54) on at leastone of said external surface and said second electrically insulatingsheet (44); and wrapping said second electrically insulating sheet (44)about said inner enclosure to encapsulate said inner enclosure.
 2. Themethod of claim 1 wherein a low tensile strength material (58) havinglower cohesion than adhesion is located between the first electricallyinsulating sheet (60) and the electrically responsive material (56). 3.The method of claim 1 wherein the electrically responsive material isprovided in the form of one or more lines (56).
 4. The method of claim 3wherein adhesive material is provided at selected edge portions (100) ofsaid first electrically insulating sheet (60) and on folding said firstelectrically insulating sheet (60) to define the inner enclosure saidselected edge portions are placed in overlapping relation.
 5. The methodof claim 4 for use in forming a box-like security enclosure (20) andcomprising the further steps of:providing the first electricallyinsulating sheet (60) with major wall forming portions (100) carryingsaid electrically responsive lines and intermediate wall formingportions (102) located between the major wall forming portions; foldingsaid intermediate wall forming portions (102) to permit said major wallforming portions (100) to define corners of a box-like enclosureincluding folding selected intermediate wall forming portions (102) toproduce electrically responsive line to electrically responsive lineinterfaces; providing first wings (104) of electrically insulating sheetextending beyond an area of said first electrically insulating sheet(60) carrying said electrically responsive line (56); and locating saidfirst wings (104) between said folded selected intermediate wall formingportions (102) to provide electrically responsive line to electricallyinsulating material interfaces therebetween.
 6. The method of claim 5comprising the further steps of:folding further selected intermediatewall portions (102) to produce electrically insulating material toelectrically insulating material interfaces; providing second wings(106) of electrically insulating sheet carrying portions of saidelectrically responsive line; and locating said second wings (106)between said folded further selected intermediate wall portions (102) toprovide electrically responsive line to electrically insulating materialinterfaces therebetween.
 7. The method of claim 5 in which saidelectrically responsive material (56) is provided over a substantiallyrectangular area of said first electrically insulating sheet (60). 8.The method of claim 4 wherein said second electrically insulating sheet(44) is wrapped about said inner enclosure with edge portions of saidsecond electrically insulating sheet in overlapping relation.
 9. Themethod of claim 8 in which the overlapping edge portions of said secondelectrically insulating sheet (44) are formed on the inner enclosurespaced from the overlapping edge portions of said first electricallyinsulating sheet (60).
 10. The method of claim 8 in which theoverlapping edge portions of said first electrically insulating sheet(60) and the overlapping edge portions of said second electricallyinsulating sheet (44) are formed of opposite hand.
 11. The method ofclaim 1 further comprising;providing said first electrically insulatingsheet (60) with lines of electrically responsive material (56, 62) oneach side, the lines (56) on one side extending obliquely relative tothe lines (62) on the other side and the lines (56, 62) beinginterconnected at edge portions of the sheet (60) to form a plurality ofconductors (LA, LB, LC, LD) so dividing the sheet into a number ofrelatively small areas that attempted penetration of the sheet (60)damages the lines (56, 62), one edge portion of the sheet including aplurality of first switch means; selectively configuring the switchmeans to connect each one of the lines (56) on one side of the sheetwith a selected one of a plurality of lines (62) on the other side ofthe sheet; and connecting ends of the conductors (LA, LB, LC, LD) to thedetecting means (80) for detecting damage to the lines.
 12. A securityenclosure (20) comprising:an inner enclosure defined by a firstelectrically insulating sheet (60) carrying a layer (56) of electricallyresponsive material on an outer side, the sheet (60) being folded andhaving edges (100)in overlapping relation and adhered to one another todefine the inner enclosure; detecting means (80) for detectingseparation of the electrically responsive material (56) from the sheet(60) and said means being located inside said inner enclosure; and anouter enclosure defined by a second electrically insulating sheet (44)wrapped about and adhered to said inner enclosure and having edges inoverlapping relation.
 13. The security enclosure of claim 12, in which alow tensile strength material (58) having lower cohesion than adhesionis located between the first electrically insulating sheet (60) and theelectrically responsive layer (56).
 14. The security enclosure of claim12 in which the electrically responsive material is provided in the formof one or more lines (56).
 15. The security enclosure of claim 12, inwhich the overlapping edges of said second insulating sheet (44) arespaced from the overlapping edges of said first electrically insulatingsheet (60).
 16. The security enclosure of claim 12, in which theoverlapping edges of said first electrically insulating sheet (60) andthe overlapping edges of said second insulating sheet (44) are ofopposite hand.
 17. The security enclosure of claim 12, in which thefirst electrically insulating sheet forms part of an outer detectionlayer (248) of the inner enclosure and the inner enclosure furtherincludes an inner detection layer the inner detection layer extendingbeyond at least one edge of the inner detection layer to provide atleast one overlapping edge of the inner enclosure with a first portion(240) in which edges of both detection layers overlie the other edges ofthe layers and a second portion (241) in which only the outer detectionlayer overlies the other edges of the layers.
 18. The security enclosureof claim 12 in which lines of electrically responsive material (56, 62)are provided on each side of said first electrically insulating sheet(60), the lines (56) on one side extending obliquely relative to thelines (62) on the other side and the lines being interconnected at edgeportions (60) of the sheet to form a plurality of conductors (LA, LB,LC, LD) so dividing the sheet into a number of relatively small areasthat attempted opening of the enclosure damages the lines (56, 62), oneedge portion of the sheet including a plurality of first switch meanswhich are selectively configured to connect each one of the lines (56)on one side of the sheet (60) with a selected one of a plurality oflines (62) on the other side of the sheet (60), and further includingconnecting means (76) for connecting ends of the conductors to thedetecting means (80) for detecting damage to the lines.
 19. The securityenclosure of claim 18 wherein the lines (56) on one side of the sheet(60) are connected to the lines (62) on the other side of the sheet (80)at spaced points (70) along the edges of the sheet (60), the points onone side of the sheet being in register with the points on the otherside of the sheet.
 20. The security enclosure of claim 19 wherein at theedge portion of the sheet provided with first switch means, each line(56) on one side of the sheet overlies a plurality of lines (62) on theother side of the sheet, a point (70) being provided on each side of thesheet at the location of each overlap, but only one point (70a) on eachline (56, 62) providing a connection.
 21. The security enclosure ofclaim 19 wherein the lines (56, 62) on opposite sides of the sheet areinterconnected at each pair of connected registering points (70a) by asemi-conductive or conductive material (74) extending through a hole(72) formed in the sheet (60) at the registering points (70).
 22. Thesecurity enclosure of claim 12 in which: lines (56, 62) of electricallyresponsive material are provided on each side of said first electricallyinsulating sheet (60), the lines (56) on one side of the sheet extendingobliquely relative to the lines (62) on the other side and beingconnected thereto at edge portions of the sheet to form a plurality ofconductors (LA, LB, LC, LD), so dividing the sheet into a number ofrelatively small areas that attempted opening of the enclosure damagesone or more of the lines (56, 62).
 23. The security enclosure of claim12 in which the first electrically insulating sheet (60) forms part ofan outer detection layer (48) of the inner enclosure and the innerenclosure includes a further inner detection layer (110), said innerdetection layer (110) comprising a third electrically insulating sheet(124) carrying lines (122, 126) of electrically responsive material oneach side, the lines (122, 126) being arranged in parallel and having awidth and pitch such that the lines (122, 126) collectively provideelectrically responsive material on said third electrically insulatingsheet (124) on at least one side over the whole extent thereof,penetration of the enclosure damaging at least one of the lines (122,126) and which damage is detectable by said detecting means (80). 24.The security enclosure of claim 23, further comprising a still furtherinner detection layer (108) similar to said further inner detectionlayer (110) and adhered thereto with the lines (123, 127) of said stillfurther inner detection layer (108) extending perpendicular to the lines(122, 126) of said further inner detection layer (110).